Effects of Hydrodynamic Forces on Ice Plate Bending Failure

本研究取得的主要成果如下：1.在冰模型水池上进行了三种不同形式的模型冰板弯曲特性试验。分别进行了悬臂梁弯曲试验、三点弯曲试验和钢板挠度试验。本文还利用刚体弹簧模型对悬臂梁弯曲试验中的问题进行了计算。结果表明，通常采用的悬臂梁弯曲试验给出的杨氏模量明显偏小，这主要是由于悬臂梁根部连接的板的挠度引起的，而悬臂梁弯曲试验给出的抗弯强度值是合适的.采用二维流场计算和梁理论对船舶推进水压力对碎冰尺寸的影响进行了理论分析。结果表明，由于冰块尺寸减小，冰板下的压力增加。这一趋势与实船和模型船的观测结果一致。破冰的力量与船速的平方成正比。现有的冰阻预测方法没有考虑这一事实.在“Soya”号破冰船上进行了全尺寸和简化船模试验，以测量破冰模式。冰的深度与其长度的比值在0.17 - 0.27之间。对于实船和模型船，较厚的冰板增大了破碎的冰块。模型和全尺寸模型中的冰块大小存在显著差异，模型中的冰块比全尺寸模型中的冰块大几倍。这种差异被认为是由于全尺寸和模型之间的冰的力学性质的差异。

The results obtained in this research are summarized as follows :1. Three kinds of model ice plate flexural property tests were performed at an ice model basin. Those were cantilever bending test, 3 point bending test and plate deflection test. Calculations using Rigid Body Spring Model were also made to investigate the problems in the cantilever bending test. The results showed that the generally adopted cantilever bending test gave significantly smaller Young's modulus mainly because of the deflection of the plate connected with the root of the cantilever while it gave proper values of the flexural strength.2. Fundamental theoretical analyses using two-dimensional flow calculation and beam theory were made to investigate the effect of water pressure due to ship advance on the size of the broken ice pieces. The results showed that the pressure increase under the ice plate due lessened the ice piece size. This tendency agreed with the observations on the full-scale and model ships. The force to break the ice increased in proportion to the square of the ship speed. This fact has not been taken into account in the existing ice resistance prediction methods.3. Full-scale and simplified ship model experiments on the icebreaker "Soya" were performed to measure the icebreaking patterns. The ratio of the ice piece depth to its length was in the range of 0.17 - 0.27. Thicker ice plate enlarged the broken ice pieces for both the full-scale and model ship cases. The size of the ice pieces were significantly different between the full-scale and the model ; the ice pieces in the model were some times larger than those in the full-scale. This discrepancy was considered due to the difference in the ice mechanical properties between the fullscale and the model.